Project Summary/Abstract Alzheimer?s Disease (AD) is a progressive neurodegenerative disease, manifesting in brain pathology, neuropsychiatric symptoms, and cognitive decline. In general, confirmatory diagnosis of AD involves both pathological hallmarks (such as plaques and tangles) as well as clinically observed cognitive decline. Whereas most cases of patients with AD pathology show cognitive and clinical phenotypes, a subset of individuals have pathology suggestive of AD without the corresponding cognitive impairment. One possible explanation is that these ?resistant? individuals have compensatory mechanisms protecting their cognitive status from the presence of pathology. Recent work from single-nucleus RNA-sequencing on post- mortem human frontal cortex tissue suggests molecularly distinct subsets of astrocytes (a non-neuronal cell type in the brain) are differentially present in ?resistant? versus ?susceptible? (cognitively declined with pathology) individuals. However, this observation so far has been limited to a single brain region in a small sample of primarily Caucasian individuals. This proposal aims to corroborate and extend this finding by investigating astrocyte subpopulations, their molecular profiles, and their associations with other cell types in multiple regions of the brain in an ethnically diverse. Through a combination of single- nucleus RNA-sequencing, spatial transcriptomics, immunohistochemistry, and systems biology, we propose to create a map of the differential distribution of astrocyte subpopulations in ?resistant? and ?susceptible? individuals, their spatial relation to pathology and other cell types, and candidate genes and pathways that involved in astrocyte-mediated resistance to tau pathology. Ultimately, characterizing the association between specific astrocyte subpopulations, their interactions, and pathways involved in resistant individuals may identify therapeutic avenues to mitigate cognitive decline in the presence of AD pathology.